Materials and Components Questions

• When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ∈'r - j∈"r . In such materials, the dielectric losses under alternating stress is proportional
• Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic. Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions tc are related as λ = vTc.
• Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment. Reason (R): The structure of CO2 is O = C = O.
• Paramagnetic materials have permanent magnetic dipoles but interaction between neighbouring dipoles is negligible.
• Assertion (A): Copper is a monoatomic solid. Reason (R): In a metal the valence electrons belong to all atoms.
• If q is charge on an electron, R is radius of electron orbit and ω is angular velocity of electron rotation, the magnetic dipole moment of electron in orbit is
• The classes of solid dielectrics are
• For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in
• Assertion (A): If WF is Fermi energy, v is velocity of electron and m is mass of electron, then . Reason (R): Conductivity of a metal depends on temperature and impurity concentration.
• The temperature below which certain materials are antiferromagnetic and above which they are paramagnetic is called
• Assertion (A): When cathode temperature is increased from 2500 K to 2550 K, thermionic emission current may increase by about 50%. Reason (R): Thermionic emission current ∝ T2 e-Ew/kT.
• Assertion (A): Silicon is the most favoured semiconductor material. Reason (R): PIV for silicon diode is more than that for germanium diode.
• Assertion (A): Magnetism can be explained by the theory of magnetic domains. Reason (R): The existence of magnetic domains is evident from the Bitter powder patterns.
• In crystalline solids, atoms are stacked in a regular manner.
• Orbital magnetic dipole moment is due to the motion of electron in its orbit around nucleus.
• In a piezoelectric crystal, the application of mechanical force will cause
• A piece of iron is placed in a magnetic field
• Assertion (A): If difference between static and optical dielectric constant is high, the mechanical compressiblity of that material is also high. Reason (R): For soft ions, ionic polarization per unit field is higher than that of hard ions.
• Assertion (A): In Figure, the intercept of the line on y-axis is equal to N (ae + ai), where N is number of atoms/m3, ae is electronic polarizability and ai is ionic polarizability. Reason (R): ae and ai are independent of temperature.
• Semi conducting materials are all